This is an R21 application intended to investigate the mechanisms of atherogenic effects of bisphenol A (BPA). BPA is a base chemical used extensively in polycarbonate plastics in many consumer products, and human exposure to BPA is ubiquitous. Higher BPA exposure has recently been associated with an increased risk of cardiovascular disease (CVD) in multiple human population-based studies. However, the mechanisms responsible for these associations remain unknown. Many environmental chemicals can activate the xenobiotic receptor pregnane X receptor (PXR) which, in turn, acts as a xenobiotic sensor to regulate xenobiotic metabolism and exhibits considerable differences in its pharmacology across species. Very recently, we revealed PXR's pro-atherogenic effects in animal models and found that chronic activation of mouse PXR increases atherosclerosis in atherosclerosis-prone apolipoprotein E deficient (ApoE-/-) mice. We also demonstrated that BPA is a potent activator of human but not mouse PXR, consequently, the choice of animal model is paramount in predicting the human risk assessment of BPA. Therefore, we generated novel PXR- humanized ApoE-/- mice (huPXR.ApoE-/-, i.e., ApoE knockout mice with the human PXR transgene in place of mouse PXR) that can respond to human PXR ligands. Our central hypothesis is that chronic activation of PXR by exposure to BPA promotes foam cell formation and increases atherosclerotic lesion formation in PXR- humanized mice, thereby increasing the risk of CVD in exposed individuals. Two specific aims are proposed to test this hypothesis: 1) Does chronic exposure to BPA at doses relevant to human exposure increase atherosclerosis in PXR-humanized ApoE-/- mice? 2) What molecular pathway does BPA act through to influence atherogenesis? The proposed studies are the first to investigate the effects of BPA exposure on atherosclerosis in a suitable animal model, and to explore the precise molecular mechanisms by which BPA induces CVD at the molecular level.